The present invention relates to a two-sided surface grinding method and apparatus for grinding the opposite surfaces of a workpiece simultaneously by a pair of oppositely disposed, rotating, grinding wheels.
As for two-sided surface grinding for simultaneously grinding the opposite surfaces of a workpiece by a pair of grinding wheels, there are an ordinary infeed grinding method and through-grinding method and besides these, there is a grinding method which is a combination of the infeed grinding method and through-grinding method (Patent Document 1: Japanese Utility Model Laid-Open 2002-307272). This grinding method performs infeed grinding by cuttingly infeeding the grinding wheels while oscillating a workpiece by reciprocating a carrier at the infeed grinding position, and then once removing the workpiece from between the grinding wheels by rotating the carrier. And through-grinding is performed by feeding the workpiece into between the grinding wheels by the feed operation of the carrier.
Conventional grinding methods are such that in infeed-grinding a workpiece while oscillating the workpiece by reciprocating the carrier at the infeed grinding position, of a plurality of workpieces circumferentially held by the carrier, two on opposite sides stick out from the outer peripheral edges of the grinding wheel surfaces of the grinding wheels. This results in a decrease in the area of contact of the grinding wheels with the workpieces, and the grinding wheel surfaces are worn to form worn wheel edges in the outer edge because of the cutting operation of the grinding wheels, etc., thereby aggravating the parallelism and flatness of the grinding wheel surfaces of the grinding wheels and decreasing the grinding accuracy. Therefore, it is necessary to correct the parallelism and flatness in a relatively short time, and there is a disadvantage that the dress interval is shortened.
And surface grinding is generally performed as shown in FIG. 11(A), wherein a workpiece 3 held in a pocket 2 in a carrier 1 is fed to pass along the inner and outer peripheral edges of the grinding wheel surfaces 4a of a pair of grinding wheels 4. In this case also, part of the workpiece 3 sticks out from the grinding wheel surfaces 4a of the grinding wheels 4, leading to a disadvantage that worn wheel edges 4b and 4c are formed in the inner and outer corners of the grinding wheel surfaces 4a as by the cutting operation of the grinding wheels 4, etc. as shown in FIG. 11(B). Particularly, in the case where the workpiece 3 which has a short cycle time and a large grinding allowance is ground, the worn wheel edges 4b and 4c in the inner and outer corners of the grinding wheel surfaces 4a become greater.
In view of such conventional problems, an object of the present invention is to provide a two-sided surface grinding method and apparatus which are capable of preventing worn wheel edges or the like in the inner and outer corners of the grinding wheel surfaces of grinding wheels, capable of maintaining the grinding wheel surfaces in proper shape for a prolonged time, and capable of prolonging the dress interval with satisfactory grinding accuracy ensured, the life of the grinding wheels being improved.